Colored heat shrinkable elastomeric tubing

ABSTRACT

This invention relates to polychloroprene based colored heat shrinkable elastomeric tubing having excellent electrical properties and to the method of manufacture.

United States Patent Ayella 1 July 4, 1972 [54] COLORED HEAT SHRINKABLEReferences Cited ELASTOMERIC TUBING OTHER PUBLICATIONS [72] Inventor:Edmond R. Ayella, Philadelphia, Pa. Murray et al. The Neoprenes (duPont)(Wilmington, Del) [73] Assignee: Penntuhe Pladics Company, v Clifton gggg 34- 77' 86- Helghts Davis et al.- Chem. & Techn. of Rubber(Reinhold) NY.) 22 Filed; ,2 1970 (1937); pages 128- 130, 705- 706, 709-7H, 715- 719.

TSl890D2J. [21] Appl. No.: 8,021 Maynard et al.-.l. Pol. Sci. I8, 227--234(1955). CD28 1 P616.

52 U.S. Cl. ..260/30.6, 260/312, 260/314 R, 260/3L8 DR, 260/415 R,260/415 A, 260/923, Finnegan Durham & Pine [51] Int. Cl. ..C0 11/02,B29C 17/07, B29C 13/00 57 ABSTRACT [58] Field of Search...............260/890, 92.3, 41.5 A, 30.6 R,

260/312 MR, 31.4 R, 31.8 DR; 264/230, 95

This invention relates to polychloroprene based colored heat shrinkableelastomeric tubing having excellent electrical properties and to themethod of manufacture.

8 Claims, No Drawings COLORED HEAT SHRINKABLE ELASTOMERIC TUBING Theinvention relates to colored heat shrinkable elastomeric articles havingexcellent electrical insulation properties and to a method of preparingsuch articles. The articles have numerous uses. For example, heatshrinkable tubing can be placed over pipe joints and can then be shrunkthereby providing a tight fitting protective cover. Another use of heatshrinkable tubing is the harnessing and jacketing of electrical wires.The articles are elastomeric, both before and after deforming, and thushave the usual advantages which this property imparts. The colorednature of the product and the ability to color the product as desired,gives an outstanding advantage in that they may be color-coded forvarious electrical purposes.

The articles are formed from a homogeneous blend of two components, (1)a cured polychloroprene elastomer, and (2) a polychloroprene elastomerhaving a Williams Plasticity Number (ASTM-D-926-56) of at least 1,000 at100 F. and less than 350 at 150 F. The amount of each component in theblend should be between percent and 90 percent (all percentages hereinare by weight) of the total blend. Preferably the amount of component(1) is 10 to 50 percent, and the amount of component (2) is 50 to 90percent.

The chloroprene polymer of component (1) can be any of the conventionalsolid chloroprene polymers, such as those marketed commercially underthe trademark Neoprene." They can be the sulfur modified chloroprenepolymers, most of these being known commercially as the G types, or can,if desired, not contain sulfur in the polymer chain, most of theselatter types being known commercially as the W" types. The uncuredelastomers of component (1) normally have a molecular weightdistribution of 20,000 to over 1,000,000 with the most abundantmolecular species being in the range of 80,000 to 250,000 (1. and E.C.,43, 154-157, 1951). The polymers are normally (before curing) soluble inbenzene. They are also solid as this latter term is defined in U.S. Pat.No. 3,147,318, with their Mooney viscosity preferably being to 65 at 158F. (ML 2.5 min.). The methods of preparing these chloroprene elastomersare well-known tothose skilled in the art; see, for example, U.S. Pat.Nos. 3,042,652; 3,147,317; 2,494,087; 2,481,044; 2,914,497; 2,567,109;and 2,831,842. More specifically, see the first chloroprene polymerpreparation described in Example I of U.S. Pat. No. 3,147,318.

Component (2) is a chloroprene polymer having a rapid change in itsWilliams Plasticity Number. At 100' F., the Williams Plasticity Numberis at least 1,000, whereas at 150 F. it is less than 350, preferablyless than 300, more preferably less than 250. Component (2) isdistinguished from the polymer of component 1) (before curing) in thatat about 150 F. its Williams Plasticity Number is lower than that ofcomponent (1), usually by at least units, whereas at about 120 F. thereverse is true, i.e., at this temperature the Williams PlasticityNumber of component (2) will be about 1,000 or higher whereas that ofcomponent 1) will be substantially less than 1,000, say 500 to 700.Preferably the Williams Plasticity Number of component (2) is about 150to 250 at 150 F. and over 1,000 at 120 F. and the Williams PlasticityNumber of component (1), before curing, is about 375 to 475 at 150 F.and 500 to 900 at 120 F.

The polymers of component (2) also have a fast rate of crystallizationas this is characteristic of chloroprene polymers having a rapid changein Williams Plasticity Number. The polymers of component (2) areprepared in conventional manner but at a polymerization temperature nothigher than about 50 F. It is well known that rapid crystallizingpolymers, i.e., those exhibiting a rapid change in Williams PlasticityNumber, are prepared at low temperatures whereas the more slowlycrystallizing polymers are usually prepared at about 1 10 to 125 F.Suitable means of preparing the polymer of component (2) are describedin Maynard et al, Journal of Polymer Science, Vol.18, pp. 227-34 (1955)and U.S. Pat. Nos. 2,417,034; 2,426,854; and 2,567,1 17. Such polymersare also widely available commercially, e.g., that marketed under thetrademark Neoprene BC" by the duPont Company.

A representative example of this component 1) polymer is one prepared inaccordance with the procedure of U.S. Pat. No. 3,147,317 and being atan-colored, soft, friable crystalline solid which melts at 104 F. to aviscous amber-colored fluid. It has a Brookfield viscosity at 122 F. of550,000 cps; 200,000 cps at 158 F. and 75,000 cps at 194 F. It has anintrinsic viscosity in benzene at F. of less than 0.15.

The articles of the invention are formed by first mixing component (1)with component (2) in any conventional rubber milling device. Duringthis mixing step, the curing agent is also added. Any of theconventional chloroprene elastomer curing agents may be employed such asmagnesium, lead and zinc oxides, alone or in combination withconventional accelerators such as Z-mercaptoimidazoline. Preferably from5 to 15 parts of zinc oxide, from 1 to 3 parts of magnesium oxide andfrom 1 to 2 parts of 2-mercaptoimidazoline are added per parts by weightof total chloroprene polymer content.

To obtain the colored electrically insulative heat shrinkable tubing ofthis invention, there should also be added to the chloroprene at themilling stage, a quantity of silica and a quantity of aluminum silicate.The silica can be added in the anhydrous or the hydrated form and willbe present in an amount, calculated on the anhydrous basis, of fromabout 15 to 30 parts, preferably 15 to 25 parts per hundred parts byweight of the total chloroprene. The silica will be in a particle sizeof not more than about 0.03 micron. The lower limit on particle size isnot critical but from a practical standpoint, the minimum particle sizewill be about 0.005 micron.

The aluminum silicate to be added to the chloroprene can also be eitherin the hydrous or anhydrous form. On the basis of the 10 percent hydrousmaterial, there should be from about 20 to 35 parts of aluminum silicateby weight per 100 parts by weight of total chloroprene. The particlesize of the aluminum silicate should be less than about 2 microns andpreferably greater than 0.005 micron.

There is also preferably added to the material during the mixing stage,particularly wherein reinforcement is desired, a quantity of calciumcarbonate within the range of about 7 to 15 parts by weight per 100parts of total chloroprene polymer.

At this mixing stage, also, particularly where low temperatureproperties are desired, a polyvinyl chloride plasticizer can be added inan amount of from about 10 to 20 parts by weight, preferably at least 15parts per 100 parts of total chloroprene polymer. Preferred plasticizersinclude dioctyl phthalate, dioctyl sebacate, butyl laurate, dibutylsebacate, di-isoctyl adipate, butyl oleate, trioctyl phosphate, thepolyether product sold as Thiokol Chemical TP9OB, butyl acetylricinoleate, tetraethyl glycol-di-Z-ethyl hexoate and tributoxy ethylphosphate.

The color is also imparted at this stage by the addition of one or moreorganic pigments compatible with the chloroprene polymers. The nature ofthe pigments and the amounts used are such as to enable development ofthe appropriate and desired color. A total of no more than about 5 partsof total pigment by weight should be used per 100 parts of totalchloroprene polymer. The lower limit will depend on the desired color.

Representative pigments include the following:

1. Ultramarine blue specific gravity 2.35

2. VS644 green MB Color lndex 74260 Phthalocyanine Pigment No. 7

3. V8825 yellow MB Color lndex 21090 Benzidine AAA Pigment No. 12

4. V8524 blue M13 Color lndex 74160 Phthalocyanine Pigment No. 15

5. V204 red MB Color Index 15630 Calcium Lithol Pigment No. 49

6. V orange MB Color Index 21110 Benzidine Pigment No. 13

1f desired, other additives desired, such as from one-half to 1% partsstearic acid as a lubricant and from 1 to 3 parts of a rubberantioxidant per 100 parts of total chloroprene, are also added in themilling step. However, it is preferred that, except as indicated herein,no other polymers other than chloroprene polymers be included in thecomposition. Chloroprene elastomers have desirable properties peculiarto themselves and these properties are usually reduced or lost by theinclusion of substantial amounts of other polymers.

After the milling step is complete, i.e., after the blend ishomogeneous, the blend is formed into the desired shape. If, forexample, heat shrinkable tubing is desired, the blend is extruded intotubing on a conventional elastomer extruder. The indicated extrusiontemperature will usually be about 170 F. but will vary from about 160 to180 F. depending upon the desired shape of the article, the compositionof the material, and the like.

The shaped blend is then cured. This is accomplished in a conventionalmanner but most extruded goods are usually cured in open steam for to120 minutes, although the time will vary depending upon such factors asthe thickness of the article and the like. Alternatively, other curingmeans such as hot air, irradiation and the like may be employed ifdesired. Although the extent of curing will vary depending upon the useto which the ultimate article is to be put, it will usually be such thatat room temperature the blend will have a tensile strength of at least500 psi, preferably at least 1,500 psi.

The shaped and cured blend is then expanded into the desired shape. Thisis effected in any convenient manner, but normally involves theapplication of air pressure or mechanical pressure while maintaining thetemperature at about 150 to 200 F, Die tubes of the required internaldimension can be used to maintain the proper expanded dimension.

1f the tubing is expanded in open air, without use of restraining meanssuch as a die tube, the tubing may be softened either by heating orthrough treatment with a suitable solvent such as methylene chloride. 1fthe tubing is softened by heating, one end of the tubing should beclamped off and then air or mechanical pressure is used to expand thetubing to the desired extent. The tubing should be allowed to cool toroom temperature before the pressure is relieved. This permits theexpanded dimension to be retained.

If a solvent is used, some of the solvent is allowed to dry out of thetubing and then the same procedure is followed.

1f the tubing is expanded through a die tube, the die tube is maintainedat a temperature between 150 and 200 F., preferably at 175 F. Air ormechanical pressure is applied at one end of the die tube while thetubing passes through the die tube, with the other end of the tubingclamped ofi. The tubing is allowed to cool to room temperature and thepressure is then released.

1n the expanded state, the article is elastomeric, i.e., it has thecharacteristic property of rubber in that it deforms under relativelysmall force but returns to essentially its original configuration whenthe force is relieved.

The expanded article can now be shrunk merely by heating. Normally,heating to about 125 F. will cause some shrinkage will full shrinkageoccurring at about 160 F. Full shrinkage means shrinking to close to theoriginal shape, i.e., the shape of the article before the expansionstep. Shrinkage will occur, depending on the temperature, in an amountsuch that the ratio of expanded to recovered diameter will be preferablyat least 1.5 and more preferably at least 2.

In some cases, it may be observed that the milling of component (1) andcomponent (2) together takes longer than is desired. This sometimesoccurs because these two components are not always as compatible as theymight be. In such cases the milling time can be reduced by the additionto the blend of a fluid chloroprene polymer. These polymers are preparedas described in U.S. Pat. No. 3,147,317 but, in general, are prepared inthe same manner as the polymer of component (1) except that a sufiicientamount of a conventional chain transfer agent is used to reduce theviscosity, say about five parts of a xanthogen disulfide per 100 partsof chloroprene. These fluid chloroprene polymers have an intrinsicviscosity in benzene at F. of less than 0.15. They can also be describedas fluid because they are pourable at 130 F. When a fluid chloroprenepolymer is used to improve the processability, it should only be used inabout 1 to 15 percent based on the total weight of the three chloroprenecomponents. Preferably, the amount used is only about 5 percent. Ratherthan use a fluid chloroprene polymer, other pourable (at 130 F.)elastomeric polymers, such as polyacrylonitrile andbutadiene-acrylonitrile copolymers, can be used, but for the reasonmentioned before, it is desirable to limit the composition topolychloroprenes.

As mentioned before, the amount of component 2) should be 10 to percent.However, the ability of the articles of the invention to retain theirexpanded shape but yet deform on heating is due to the presence ofcomponent 2). Accordingly, in all cases, the amount of component (2)should be sufficient to achieve this characteristic, that is, ifinsufiicient component 2) is used, it will not remain expanded, or,stated in another manner, it will not permit deformation by heat.

The tubing may be crosslinked, if desired, by conventional means.Crosslinking before expansion will generally permit a greater degree ofexpansion of the tubing of this invention. Any conventional means knownfor use in crosslinking chloroprene polymers such as, for example, theuse of irradiation and the use of chemical crosslinking agents, may beemployed. Where chemical crosslinking agents are employed, thecrosslinking action may be accelerated by heating, as, for example, at atemperature of from 250 to 310 F. for from 20 minutes to 2 hours.

The following examples are illustrative of the invention with all partsbeing by weight:

EXAMPLE I This example illustrates the preparation of green colored heatshrinkable tubing. Preparation of Component (2) Component (2) describedpreviously is prepared as follows: An emulsion of chloroprene parts),dodecyl mercaptan (0.2 part), disproportioned rosin (5 parts), water 150parts), caustic soda (0.75 part), sodium salt of formaldehydenaphthalenesulfonic acid condensate (0.5 part), and sodium sulfite (0.5 part) isprepared. Polymerization is effected in a conventional reactor and undera nitrogen atmosphere by the addition of 3 parts of catalyst which is amixture containing 1.2 percent potassium ferricyanide and 98.8 percentwater. Catalyst is added slowly while maintaining the polymerizationtemperature at 32 F. At about 90 percent monomer conversionpolymerization is stopped by the addition of a mixture of phenothiazineand 4-tert-butylcatechol. The latex is then stabilized by the additionof 1.5 parts water, 0.2 part sodium laurylsulfate, 1.5 parts tetraethylthiuram disulfide, 2 parts toluene, and 0.05 part of the sodium salt offormaldehyde-naphthalene sulfonic acid condensate. Unreacted chloropreneis removed by steam stripping, the polymer is acidified with acid, andis then removed by freeze coagulation. The polymer has a WilliamsPlasticity Number at 100 F. of over 1,250, at 150 F. of 240, and at F.of greater than 1,000.

Preparation of Component 1 A polymer suitable as component (1) isprepared as in Example of U.S. Pat. No. 3,147,317. This preparation issubstantially the same as in the preparation of component 2) above,except for the catalyst employed and the polymerization temperature. Thelatter is 122 F. and this results in a polymer which does not have theplasticity-crystallization characteristics possessed by the polymerprepared in Example 1. The polymer has a Williams Plasticity Number inexcess of 1,000 at 100 F. but it is also well in excess of 500 at F,Blending The following materials are blended in a conventional rubbermill at 150 F. for 30 minutes.

Parts by Weight chloroprene component (2) 67.5 chloroprene component (1)25.0 butadiene acrylonitrile copolymer (Hycar 1312) 5.0 magnesium oxide2.0 stearic acid 0.5 2,2 methylene bis(4-methyl- 6t-butyl phenol) 1.5hydrated aluminum silicate 25.0 hydrated silica 25.0 calcium carbonate10.0 Vansul VS-644, green pigment 0.5 ultramarine blue 1.0Z-mercaptoimidazoline 1.5 zinc oxide 10.0 dioctyl phthalate 16.0

Extruding and Expanding After blending, the mixture is extruded at 160to 180 F., preferably about 170 F., into tubing having an I. D. ofonehalf inch and a wall thickness ofO. 150 inch. The tubing is thencured for twenty minutes with 60 psig. steam. Finally, air pressure isused to expand the tubing to 2'inches l. D., the expansion beingconducted with the tubing heated to between 150 and 200 F., preferablyabout 175 F., and one end pinched closed and the other connected to anair supply. A die tube was used to control the size of the expandedtubing. It is, however, not essential. The tubing is water-cooled toroom temperature, the air pressure then released, and the tubing staysin the expanded form. The expanded tubing is elastomeric. When air at170 F. is blown on the tubing, it immediately shrinks within severalseconds to an I. D. of one inch or less. The shrunken tubing is alsoelastomeric.

EXAMPLE 11' This example is the same as Example I except the polymerused as component (2) is the commercially available polymer known asNeoprene HQ" and the polymer used as component l) is the commerciallyavailable polymer known as Neoprene AC.

The electrical properties of the green tubing prepared in accordancewith this example are as follows:

dielectrical strength ASTM-Dl49 886 volts/mil volumeresistivity-ASTM-D257 5.1 X ohm-cm dielectric constant ASTM-DlSO 2.63heat resistance 24 hrs. at 100 C.

followed by test for dielectric strength 860 volts/mil fluid resistance24 hrs. at 24 C.

in following:

dielectric strength hydraulic fluid Mil-H-S606 880 volts/mil J P 4 fuel900 lube oil Mil-L-7808 870 lube oil Mil-L-23699 1010 5% sodium chloride890 .de-icing fluid Mil-A-8243 860 For Color Substitute in FormulationParts by Weight Yellow Vansul VS-825 Yellow MB 1.0 Blue Vansul S524 Blue1.5 Red Vansul V204 Red MB 1.0 Orange Vansul V-l05 Orange MB 1.5

EXAMPLE 111 The procedure is the same as in Example 11 except that 7.5parts of a fluid chloroprene polymer commercially available as NeopreneFC having a Brookfield viscosity of 550,000 at 1 22 F. is added to themill in place of the Hycar 1312. Similar results are obtained. The blendon milling becomes uniform less rapidly but results are otherwisesimilar if both the l-lycar l 3 l 2 and the Neoprene FC are completelyomitted.

I claim:

1. Colored, heat shrinkable elastomeric tubing having excellentelectrical properties comprising a cured mixture of two chloroprenepolymers and, per 100 parts by weight of total chloroprene polymercontent, from about 15 to 30 parts by weight of silica, from 20 to 35parts by weight of aluminum silicate and up to 5 parts by weight of apigment, said chloroprene polymers comprising (a) from about 10 topercent by weight of a curable polychloroprene elastomer, and (b) fromabout 10 to 90 percent by weight of a polychloroprene elastomer having aWilliams Plasticity Number at F. in excess of 1,000 and at 150 F. ofless than 350, said tubing being further characterized in that upon theapplication of heat it will shrink but retain its elastomeric character.

2. Tubing according to claim 1 wherein the Williams Plasticity Number of(b) at 150 F. is less than 300.

3. Tubing according to claim 1 wherein the amount of (b) is 50 to 90percent and the amount of (a) is 10 to 50 percent.

4. Tubing according to claim 1 wherein the Williams Plasticity Number of(b) at 150 F. is at least 50 units less than the Williams PlasticityNumber at 150 F. of (a) before said curing.

5. Tubing according to claim 1 further characterized in that theWilliams Plasticity Number of (b) at F. is at least 1,000 whereas theWilliams Plasticity Number of (a) before said curing is substantiallyless than 1 ,000.

6. Tubing as in claim 1 also containing from about 7 to 15 parts byweight of calcium carbonate per 100 parts of total chloroprene polymer.

7. Tubing as in claim 1 also containing from about 10 to 20 parts byweight of a polyvinylchloride plasticizer per 100 parts of totalchloroprene polymer.

8. Tubing as in claim 1 being further characterized by a ratio ofexpanded to recovered diameter of at least 2.

mil.

2. Tubing according to claim 1 wherein the Williams Plasticity Number of(b) at 150* F. is less than
 300. 3. Tubing according to claim 1 whereinthe amount of (b) is 50 to 90 percent and the amount of (a) is 10 to 50percent.
 4. Tubing according to claim 1 wherein the Williams PlasticityNumber of (b) at 150* F. is at least 50 units less than the WilliamsPlasticity Number at 150* F. of (a) before said curing.
 5. Tubingaccording to claim 1 further characterized in that the WilliamsPlasticity Number of (b) at 120* F. is at least 1,000 whereas theWilliams Plasticity Number of (a) before said curing is substantiallyless than 1,000.
 6. Tubing as in claim 1 also containing from about 7 to15 parts by weight of calcium carbonate per 100 parts of totalchloroprene polymer.
 7. Tubing as in claim 1 also containing from about10 to 20 parts by weight of a polyvinylchloride plasticizer per 100parts of total chloroprene polymer.
 8. Tubing as in claim 1 beingfurther characterized by a ratio of expanded to recovered diameter of atleast 2.